The invention generally relates to implantable stimulation devices such as cardiac stimulation devices, cardioverters and defibrillators. More particularly, this invention relates to an implantable stimulation system having a single-pass lead which delivers stimulation therapy and is capable of a plurality of programmable sensing polarities, including bipolar atrial and ventricular sensing with respect to an electrode positioned near the tricuspid valve.
Implantable stimulation devices, such as cardiac stimulation devices and implantable cardioverter-defibrillators (hereinafter referred to as ICDs), are often used to remedy improper heart function. These devices generally provide an electrical pulse to a selected area of the heart that is not (in terms of timing or strength) adequately receiving its natural pulse. Under abnormal cardiac conditions, and particularly cardiac rhythm disturbances, stimulation therapy is applied to remedy several forms of cardiac arrhythmias (rhythm disturbances) including bradycardias, AV conduction block, supraventricular tachycardias, and atrial and ventricular ectopic arrhythmias.
There are essentially two kinds of stimulation devices: single-chamber and dual-chamber. Single-chamber stimulation devices are capable of sensing and pacing in only one of the atrium or the ventricle. Dual-chamber stimulation devices are capable of sensing and pacing in both the atrium and the ventricle. There are many modes of dual-chamber pacing such as VDD (paces in the ventricle only, senses in the atrium and ventricle), DVI (paces in the atrium and ventricle, and senses in the ventricle only), DDI (senses and paces in both the atrium and ventricle), and DDD (senses and paces in both the atrium and ventricle, with an inhibited and triggered response to sensing).
A letter xe2x80x9cRxe2x80x9d is sometimes added to these stimulation device modes to indicate the stimulation device""s ability to provide rate-modulated (also sometimes called rate-responsive or rate-adaptive) pacing in response to input from an independent sensor. For instance, a DDDR stimulation device is capable of adapting to the need to increase a patient""s heart rate in response to physiologic stress in the absence of intrinsic response from a patient""s sinus node.
Dual-chamber ICDs are also known in the art to proved pacing, cardioversion and defibrillation therapy in both chambers of the heart.
A stimulation device uses a lead system to perform its sensing and stimulation functions. A lead system typically comprises at least one lead, one or more conductor coils, and one or more electrodes. The lead is the insulated wire used to connect the pulse generator of a stimulation device to the cardiac tissue. The lead carries the output stimulus from the pulse generator to the heart and, in demand modes, relays intrinsic cardiac signals back to the sensing circuitry of the stimulation device. Typically, a single-chamber stimulation device requires one lead, whereas a dual-chamber stimulation device requires two leads (one for the atrium and another for the ventricle). The conductor coil is the internal core of the pacing lead through which current flows between the pulse generator and the electrodes.
A lead may be unipolar or bipolar. A unipolar lead is a pacing lead having one electrical pole external to the pulse generator, which is usually located in the heart. The unipolar lead has one conductor coil. The electrical pole is typically a stimulating cathode (i.e., negative pole) at the distal tip of the lead. As used herein, a distal end of the lead is the end which is farther away from the stimulation device. A proximal end of the lead is the end which is connects to the stimulation device. The cathode is the electrode through which a stimulating pulse is delivered. The anode electrode (i.e., the positive pole) is the case, or housing, of the stimulation device. A stimulating pulse returns to the anode using the body tissue as a return current path. A unipolar lead is relatively small in size and is theoretically more reliable than a bipolar lead. However, a unipolar lead/pacing system is more susceptible to interference by other electrical activity in a patient""s body, such as inhibition due to myopotentials, and further may be prone to pectoral stimulation.
On the other hand, a bipolar lead is a pacing lead with two electrical poles that are external to the pulse generator. The bipolar lead has two conductor coils. The stimulating cathode is typically at the distal tip of the pacing lead, while the anode is an annular (i.e., ring) electrode which is few millimeters proximal to the cathode. As such, bipolar leads are less prone to pectoral stimulation. A bipolar lead has better signal-to-noise ratio than that of a unipolar lead, and thus, is less susceptible to interference from myopotential inhibition.
In practice, the cathode (i.e., stimulating) electrode is typically placed in contact with the heart tissue in order to stimulate the cardiac tissue. The anode electrode, however, does not need to be in contact with the heart tissue, since blood tends to conduct electrical currents better than the tissue itself. Nonetheless, it is preferable to have the sensing electrode in contact with the heart tissue to allow the detection of more distinct signals. For more details on bipolar lead structure and electrode placement, reference is made to commonly-assigned U.S. Pat. No. 5,522,855, issued to Hoegnelid on Jun. 4, 1996, and is incorporated herein in its entirety by reference. Moreover, for details on quadrapolar (four electrodes) lead structure and electrode placement, reference is made to commonly-assigned U.S. Pat. No. 5,304,219, issued to Chemoff et al. on Apr. 19, 1994, and is incorporated herein in its entirety by reference.
While bipolar leads are reknown for their improved sensing characteristics, some physicians still prefer unipolar leads since the additional stiffness of the bipolar leads makes them handle differently. Programmable polarity has the known advantage of permitting physicians the ability to implant the leads of choice and stock only one stimulation device model that can handle both leads. Further, if bipolar leads are initially implanted, the polarity can be modified based on the patient""s needs.
There has been a long felt need to simplify the implantation of dual-chamber stimulation devices by using only one lead, commonly referred to as a xe2x80x9csingle-passxe2x80x9d lead. The earliest known single-pass leads was a xe2x80x9cmulti-polarxe2x80x9d device (1974) by Berkovits (U.S. Pat. No. 3,825,015) in which two electrodes were placed in the ventricle and four electrodes were placed in the atrium, however, only the best two of the four atrial electrodes were used ultimately.
xe2x80x9cQuadrapolarxe2x80x9d leads (1975) were attempted by Woollons et al. (U.S. Pat. No. 3,903,897) in which two electrodes were located in the apex of the ventricle and two xe2x80x9cfloatingxe2x80x9d electrodes in the atrium. However, these leads were very stiff, and positioning the atrial electrodes to make contact were difficult.
Both of these systems were extremely stiff, and either had poor contact with atrium or had extremely large, complicated connectors.
One of the simplest single-pass leads was a two-electrode lead (1979) by O""Neill (U.S. Pat. No. 4,154,247) in which an electrode was placed in each of the atrium and the ventricle.
Of course, pacing thresholds were also improved upon by forcing the atrial electrode(s) to make direct contact with the cardiac tissue. This may be achieved by either pre-forming the lead in the region of the atrial electrode (as in the ""247 patent, supra) or by using various anchoring or active fixation techniques by Grassi (U.S. Pat. No. 4, 624,265) and Hess (U.S. Pat. No. 4,664,120).
Later, xe2x80x9ctripolarxe2x80x9d electrodes were developed with two electrodes in the apex of the ventricle and a single electrode in the atrium (see U.S. Pat. No. 4,585,004 to Brownlee). Other attempts at tripolar electrodes included a single electrode in the ventricle, with two electrodes in the atrium (see U.S. Pat. Nos. 4,711,027 (Harris); 4,962,767 (Brownlee); and also 5,172,694 (Flammang)).
These tripolar leads of the prior art are chosen since they permit synchonicity between the atrial and ventricular chambers of the heart while providing a less stiff lead, with a smaller proximal connector (which affords a small, less complicated connector on the stimulating device) and without resorting to implanting an additional lead.
For purposes of delivering high voltage shocks, a xe2x80x9cdefib leadxe2x80x9d typically has at least one, and preferably two, transvenously placed shocking coils. While sensing may occur between a ventricular tip electrode and a ventricular ring electrode, it is also known to sense in an xe2x80x9cintegrated bipolarxe2x80x9d fashion between the ventricular tip and a ventricular coil electrode (or between the atrial electrode and an SVC coil electrode).
However, these prior art leads do not offer full programmability of the electrode polarity with a simplified lead structure for ease of manufacture and improved reliability. Accordingly, there is a need in the cardiac pacing technology to offer a lead system which offer programmability, is compactly structured, can be easily placed in a patient""s heart and, therefore, is inherently more reliable.
To overcome the above-mentioned problems, the invention provides an improved single-pass lead comprising three electrodes suitable for sensing intrinsic cardiac activity in two chambers of the heart, for stimulating cardiac tissue in at least the ventricle, and having programmable unipolar or bipolar polarity.
In a first embodiment, suitable for use in an implantable pacemaker having a xe2x80x9cVDDxe2x80x9d mode, one tip electrode is located at the distal end in the ventricle, one ring electrode is xe2x80x9cfloatingxe2x80x9d in the atrium, and a second ring electrode is positioned near or just below the tricuspid valve.
In a second embodiment, suitable for use with an implantable cardioverter-defibrillator device, one tip electrode is located at the distal end in the ventricle, one ring electrode is xe2x80x9cfloatingxe2x80x9d in the atrium, and the second electrode is a coil electrode positioned in the ventricle proximal to the tip electrode and extends near or just below the tricuspid valve.
Hereinafter, the second electrode will be referred to as the xe2x80x9ctricuspid electrodexe2x80x9d, regardless of the type or exact construction, and will be construed to cover any electrode in proximity to the tricuspid valve.
Ventricular pacing and sensing can occur in a unipolar fashion from the distal tip electrode to the stimulation device housing (also known as the case electrode), or in a bipolar fashion from the tricuspid electrode to the ventricular tip electrode.
Atrial sensing can be achieved in a unipolar fashion from the atrial ring electrode to the housing, or in a bipolar fashion from the atrial ring electrode to the tricuspid electrode.
While the preferred embodiment is directed toward a lead suitable for VDD pacing and sensing, the present invention could be adapted to include DDD pacing and sensing if the atrial ring electrode/lead body was dimensioned so as to make contact with cardiac tissue, such as near the SA node or the atrial appendage, by preforming the lead in the region of the atrial ring electrode.
Advantageously, sensing of atrial and ventricular cardiac signals is enhanced, since the dipole created between the tricuspid electrode and either the ventricular tip electrode or the atrial ring electrode is larger (i.e., the electrodes are separated by a larger distance than standard bipolar lead arrangements). The present invention thereby detects a larger differential signal than conventional bipolar leads, is immune to myopotential signals, and still is less likely to cause pectoral stimulation.
Furthermore, the single-pass lead of the present invention adds only one additional conductor and electrode to a conventional bipolar lead, and thus is easier to implant, more reliable, and also easier to manufacture.